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Network Cable Ratings and Jacket Type Comparison
Few people give much thought to the outer jacket on network cables. However, jacketing, also known as sheathing, is vitally important to fire safety and the proper functioning of the cable.
It is also more complex than one might think. Multiple types of jacket material are used for copper cables to meet various fire ratings, and the U.S. has different cable jacket material standards than the E.U. and much of the rest of the world. Fiber-optic cables follow different standards than copper, although the E.U. allows the use of the same type of jacket material for both.
What Is a Cable Jacket?
As the name implies, the cable jacket is the outer layer. In a copper cable, the jacket covers a shielding material, which covers a layer of insulation, which covers the copper wires. In a fiber-optic cable, the jacket covers a later of strengthening fibers, which covers a primary coating, which covers glass cladding, which covers the optical fibers themselves. The cable jacket’s primary purpose is to protect the cable’s insulation and core from damage and deterioration.
What Is a Cable Sheath?
Cable sheath is another way to describe the cable jacket. It is the outermost layer of the cable protecting the cable’s insulation and core from damage and deterioration.
Different cable materials can be used for different applications. Cable jackets may be color-coded for identification. Cable jacket material selection all depends on your requirements. The different types of network cable ratings serve specific purposes. We’ll explore below.
U.S. Fire Ratings for Copper Cable Sheath Types
In the U.S., there are three common ethernet cable fire ratings: Communications Multipurpose (CM), Communications Multipurpose Cable, Riser (CMR), and Communications Multipurpose, Plenum (CMP). They are distinguished by the type of material used for the cable jacket.
“Risers” are the vertical shafts between the floors of a building. “Plenums” refer to dropped ceilings, raised floors, and other air spaces.
Communications Multipurpose Cable Fire Rating
Jackets for CM-rated cables are made from polyvinyl chloride (PVC) because it’s flexible and inexpensive. The jacketing must pass the flame test described in the UL 1865 standard. However, the PVC material can produce thick smoke and dangerous gases in a fire and may not be used in risers or plenums.
Communications Multipurpose, Riser Cable Fire Rating
Low-smoke PVC and fluorinated ethylene polymer (FEP) are used for CMR cable jackets. These materials are more flame-retardant than PVC and produce less smoke. CMR jacketing must pass the UL 1666 flame test, which is much stricter than the UL 1865 test used for CM cable jackets. The goal is to reduce the risk of the cable spreading fire from one floor to another.
Communications Multipurpose, Plenum Cable Fire Rating
CMP cable jackets are made from PVC, FEP, or other materials. Whatever material is used must pass the test defined in the NFPA 262 standard, which requires limited flame travel and low smoke.
E.U. Fire Ratings for Copper Cable Sheath Types
Low Smoke Zero Halogen (LSZH) is typically used for copper cable sheathing in the E.U. and many other parts of the world. It is also called Low Smoke Halogen Free (LSHF). The halogen in this instance is chlorine — LSZH cable jackets are made from polyethylene, which contains little to no chlorine. In a fire, polyethylene produces a limited amount of smoke and almost no hydrogen chloride, which is the most dangerous of the halogen gases.
Fiber-Optic Cable Jacket Types
For fiber-optic cables, the most common standards are Optical Fiber Nonconductive Riser (OFNR) and Optical Fiber Nonconductive Plenum (OFNP). The OFNR standard has nothing to do with the jacket materials — it refers to a cable made of non-conductive materials. The OFNP is similar to OFNR but has a jacket made of a material suitable for plenum spaces.
In the E.U., fiber-optic cables also use the LSZH material for sheathing. However, some E.U. customers prefer to follow the OFNR and OFNP standards.
Enconnex Can Meet Your Cabling Needs
Enconnex offers a plethora of network cables and accessories, including copper and fiber-optic cables to support a wide range of use cases. Our cabling experts are here to help you choose the right solutions for your requirements; just get in touch.
Posted by Mike Chen on August 5, 2022
Mike has 20+ years of senior program management, product management, and consulting experience in IT, consumer electronics, and communication products, both at finished goods and components levels. Mike is the Product Manager for Network Cabling at Enconnex.